Electrical cutting of metals



P. A. E. ARMSTRONG ELECTRICAL CUTTING OF METALS Filed July 5, 1921 5 Sheets-Sheet 1,481,854 P. A. E. ARMSTRONG Jan. 29, 1924.

ELECTRICAL CUTTING 0F METALS Filed July 5, 1921 i5 Sheets-Sheet 3 via-* Svweutoz Jan. 29 1924. 1,481,854

P. A. E. ARMSTRONG ELECTRICAL CUTTING OF METALS Filed July 5, 1921 a Sheets-Sheet 3 Patented Jan. 29 1924.

V UNITED STATES PM A. I. ABISTBONG, O1 LOUDONVILLE, HEW You.

ELECTRICAL CUTTING OI METALS.

Application flied July 5,

Toallw homitmagcmwemr Be it known t at I, Pmcr A. E. ARM- STRONG, a subject of the King of Great Britain, and a resident of Loudonville, county of Albany, and State of New York, have invented a new and useful Improvement in .Electrical Cutting of Metals, of which the following is a specification.

The present invention has for its principal object to secure rapid and efiicient electrical cuttin of metals. 1

In t e cutting of metal by the electric arc, as heretofore practiced,the arc is readily short-circuited or extinguished by the electrode coming into contact with the metal being cut, and it is a matter of considerable .diflicultyto strike the necessary balance of distance between the electrode and the metal, that is to say, to keep the electrode far enough away from the metal being cut to prevent short-circuiting and extinguishing the are on the one hand, and on the other hand to keep the electrode sufliciently close to the metal to obtainan effective are having the requisite cutting power. Furthermore, the path of the arc is uncertain, and the arc is readily deflected, and the cut thus made is broad, and the cut surface produced vis irregular and by no means as well defined as is desirable in order to compete with cutting by the oxy-acetylene flame, for example. The are for electrical cutting, as heretofore practiced, is sputtering and difficult to man age and requires comparatively high voltage, a out 45 to 50 volts, by reason of the gap which must be maintained in order to prevent short-circuiting of the arc, with consequent reduction of efiiciency by reason of lowered amperage.

According to the present invention, the cutting electrode is ut directly against the metal to be cut so that no nice distinctions of precise guiding are encountered, and the cutting appears to be. performed partially by the electrical arc and partially by the melting away of the adjacent portions of the metal as the current passes to the metal being operated upon. The voltage can be comparatively low and the operation much safer than heretofore. As low as 20 volts or lowermay be used with relatively high amperage, say about 1500 to 2000 amperes. In order to accomplish cutting under these circumstances it is necessary that the surface of the cutting electrode in contact with the 1921. Serial Io. 483,531.

' metal be of relatively small dimension and that the cross-section of the electrode shall be relatively large, so as to effectively deliver the current at the small area cutting contact at a sufliciently great current density. I have found, for example, that with a good graphite electrode havin a thickness of about g" to and a wi h of about 2" to 3" and with a current of the voltage and amperage above referred to, a practically clean out can be made of a width only slightly in excess of the thickness of the electrode, b pushing or pulling one edge or corner of t e electrode in contact with the metal and advancing it gradually as the cutting progresses. A slight up and down motion similar to the movement of a handsaw is of advantage in tending to prevent the slight progresslve burning away of the material of the electrode from being too I reatly localized, and when the electrode is" eing pushed down upon the work as in cutting a channel or groove which is deepened to a deep cut by a repeated crossing, the end or corner of the electrode may be the portion in contact with the metal, but the electrode is tipped in such case with respect to the metal so as to confine the contact area to the necessary small dimensions. While a single electrode is here referred to for convenience, it will be understood that with polyphase current, for example, a plurality of cutting electrodes may be used.

Ordinarily it is not necessary to make special provision for removal of molten metal or slag as the cutting progresses, since when the cut goes all the way through the molten metal or slag simply drops down, and even when cutting is on the top of a flat surface the molten material is thrown out in the form of aspray, but it may be of advantage to arrange the work, particularly where the cutting is heavy, on an incline, or vertically, so that any molten metal or slag which is not actually ejected from the cut may have an opportunity to run away as fast as it is formed.

\Vithout conimiting myself to any particular theory of the cutting action which appears to comprise a combination of are cuttingand of direct melting by pasage of the electrical current, I prefer to refer to the same as cutting by submerged arc. The small area contact portion of the electrode appears to accomplish a combined are cut:

ting action and a direct melting action as the cutting progresses, the metal melting away in more or less uneven form ahead of or slag as the cutting progresses, and as fast as one or more of these is melted away other spines or projections are formed or left, which are contacted by the advancing electrode and melted, and so on, and the melted metal or slag is either thrown or runs out as fast as formed, and in this way shortcircuiting or extinguishing ot' the are is pre-' vented. While the action obtained of melting by the passage of a current of high amperage in combination with the arc is preferably referred to as a submerged arc, this expression is not necessarily to be interpreted as describing an are formed within the molten metal or slag, though such action may takeplace to some extent. Atany rate the arc is maintained while the electrode is being held lightly against the metallic material which is operated on, so long as there is a fall of potential between the electrode and the work. The cut formed is somewhat wider than the thickness of the electrode since at the edge of the advancing electrode the metal is burned out on each side as far as the voltage will carry the current. With about 25 volts the cut made is usually from about to about iof an inch wider than the edge of the electrode.

It will be understood, of course, that it is possible to short circuit the are by holding the electrode hard against the work, particularly where there may be extended contact, as when a deep slot or cut is being made, as in such case the result would be much the same as if the electrode were clamped or bolted to the work, and I do not intend to include contact of such character in stating that the electrode may be in contact with the work. lVhat I wish to have understood is that it is not necessary to keep the electrode out of contact with the work and at some particular given distance therefrom, but that it may be held or pushed or pulled lightly in contact with the work as the cutting proceeds in the manner described.

The width of cut, slightly greater than the thickness of the electrode, is such that it is readily possible to keep the following portion of the electrode back of the narrow advancing edge away from the walls of the cut, and so long as this is done there is practically no arcing here by reason of the air gap and the use of low voltage current. A slight air gap is sufiicient to prevent the low voltage current jumping across. Also the oxide or slag formed on the cut surface of the metal is suficient to gresses.

prevent passage of the current or arcing to any considerable extent. Even if this rear portion of the electrode does contact with the walls of the cut to some extent occa sionally, because of wobbling of the holder in-the hands of the operator, for example, no substantial harm is done, and no difficulty is encountered in keeping the cutting action substantially confined to the area at the advancing edge of the electrode.

I have found that it is desirable to fix a maximum current. This may be done in various ways. as by the introductionof regulable resistance where direct current is used, or introduction of a resistance or reactance or both in theprimary or secondary line or both where alternating current is used, since unless this be done too great a current may pass making the action of the are unduly'hard to govern as the work pro- Such resistance or reactanoe is preferably adjustable according to the class of work and the constitution of the material being operated on. For example, where the material being cut has a high resistance of its own, the resistance may be principally or largely in the work itself and it is possible to dispense with additional resistance in the line, but where the material being out has a high electrical conductivity, the provision of resistance or rcactance to set a maximum limit for current is of substantial advantage. The electrode or electrode holder may be utilized tov provide resistance, if desired.

Apparatus for electrical cutting in accordance with my invention is diagrammatically illustrated in the accompanying drawings in which Fig. l is a part side and part diagrammatical view of apparatus adapted for alternating'current, with the electrode shown in cutting position. Fig. 2 is a plan view partly in section ShOWing how cuts are made on heavy work. Fig. 3 is a section on line 33, Fig. 2. Fig. 4 is a section on line 4-4:, Fig. 1. Fig. 5 is a part plan and part sectional view showing a modified form of electrode adapted for use in making curved cuts, Fig. 6 is a wiring diagram fordirect current, Fig. 7 is a diagrammatical view showing a modified arrangement for alternatingcurrent, Fig. 8 is a further modification showing use of an A. C. generator, Figs. 9, 10 and 11 are wiring diagrams for some of the various types of alternating current.

Fig. 12 is a side view ofa water-cooled electrode in use for making a cut. Fig. 13 IS a terchangeability of electrodes. To the work 14 to be cut is attached in any suitable manher, as by a clamp, one end of an electrical connection 15, the other end of which is attached to one terminal of a secondary circuit 18, of a transformer 17. To the other terminal 18 of the secondary circuit is attached one end of an electrical connection 19. the other end of which is attached in any suitable manner to the clamp of electrode 10. Switches 2d and 21 are shown in both the primary and secondary circuit, but the latter may be dispensed with, if desired.

Resistance or impedance or both are provided to govern the amount of current flowing by fixing an adjustable maximum limit therefor, and to give persistency to the operation. Same may be variously arranged and supplied. in the form of Fig. 1, resis ance R and impedance I areprovided in the secondary circuit. In the arrangement of F 7 resistance and impedance are provided the primary transformer circuit and resistance also in the secondary circuit. In some cases resistance may be in the elec trode or holder or in the work itself, where the material to be cut is of such character as to supply the desired resistance, so that provision of separate resistance devices may sometimes be dispensed with but reactance is practically always desirable.

While the use of a transformer is usually the more convenient practice the alternating current used may be supplied in other ways,

' as for example, the use of an alternating current generator 23 of low potential is shown diagrammatically in Fig. 8. By the use of a self regulating generator auxiliary resistance or reactance may be dispensed with, except that either or both resistance and reactance may be provided in order to accommodate various ran es of work. Direct current'may be used as illustrated in Fig. 6 in which the current is supplied by a dynamo 23 producing a standard constant potential circuit oflow voltage, and the maximum current limit is obtained by means of the rheostat R. The use of alternating current is usually preferable. however.

The cutting electrode 10 may advantageously be of good quality graphite, thou h other materials can be used, as for examp e mixtures of graphite with mineral oxide 0 high melting point, such as oxide of zirconium and the like. Mixtures of graphite with carborundum' and the like can be used. Such cutting electrode may have a substantial base 10 preferably of cylindrical form adapted to fit in the clamp 11 and a working portion 10" which is narrow in one direction and broad in the other, as for example, it may have a substantially rectangular section 10 for straight cuts as shown in Fig. 4, or may be curved in cross-section as shown at 10 Fig. -5 for making curved cuts.

In cutting the narrow dimension is in contact with the work and the cutting takes place in the small area contact section as indicated at 10, for example, Fig. 5,, and as the cuttin advances this narrow ad'vancing edge is a vanced and kept in contact with the work.

In making deep cuts a corner of the electrode is used as shown in Figs. 2 and 3 to produce successively deeper grooves, the shallow groove24 in Fig. 2 being produced by the first passageof the electrode and a deeper groove 25 by the second passage, etc., until the cut is completed. It will be understood that the various modes of cutting shown are illustrated only and that cuts may be made in various ways so long as the elect-rode is of suflicient dimension to carry deliver the necessary current density to the small area cutting section without undue heating or burning oil of the electrode between the clamp and the cutting point. In making a cut through a sheet or plate of metal at a single pass, as indicated in Fig. 1, the material of the electrode usually tfies on the form shown by the dotted line 10 and, if desired, the electrodes eriginally be made of this or similar form, as is illustrated Fig. 1. If electrodes of cylindrical or pencil section were made use of, for example, in place of the electrodes shown and described having a width several times the thickness, the electrode would be quickly destroyed and cutting in any commercial sensewould be entirely impractical.-

The electrode, instead of being moved or operated by hand, may be mechanically moved relatively to the work. Where such machine cutting is carried on, I preferably make the permanent portion of the electrode of metal as copper, preferably watercooled, and make the preferably graphite portion thereof which comes into contact with the work removable and replace-able. In Figs. 12*14 an electrode of this character is shown comprising copper bar having a passage 3]. for circulation of cooling fluid and provided with a dovetail 32 on one edge. The working surface 34 is on the electrode section 35 made of graphite or other suitable material and provided on its back edge with an undercut groove 36 adapted to be secured to the bar 31 as by r the groove 36 being run on the dovetail 32. In this way the necessary current density is delivered to the working face without undue heating of the electrodeand the graphite or like member 35 is cooled to a considerable extent by being in contact with the water-cooled section 30. While best adapted for machine cutting in which the electrode is mechanically moved with respect to the work or vice versa, such electrode may be made use of in a holder for hand cutting, if desired.

' sible exemplifications are shown in I or four wire type.

Also combinations of direct current and alternating current may be used and when the cutting electrode is motor driven the direct current through the electrode may be used to actuate or control the motor drive,

instead of using alternating current with a transformer, pulsating direct current may be supplied to the primary winding of the transformer and various other arrangements may be resorted to.

The cutting electrode may be operated mechanically instead of manually, if desired, and in Fig. 15 it have shown a motor driven electrode with alternating current control. The current is taken through a transformer from line wires 51, 52, and the wires 53, 54 connected to the secondary of the transformer supply the current for electrical cutting, being connected to the electrode 55 and work 56 respectively. A switch 57 is provided in the line, and also current control means such as reactance 5 8 or resistance 59 or both. v

The electrode is shown carried by a rack 60 which is driven from the motor 61 through suitable reducing gearing comprising' in the form shown, a-bevel pinion 62, a bevel gear 63, meshing with pinion 62, and the rack pinion 64 on the same shaft with the gear 63. The motor arrangement is such that the motor feeds the cutting electrode relatively to the work at a rate to percases the transformer may not be required.

In the form shown, the motor current wires 66, 67 take current from, the secondary of transformer 65, switch 68 being closed, but

if switch 68 be opened and switch 69 closed the transformer is out out and the cutting current is used for the motor drive.

A voltage coil 70 in the motor circuit is made use of to actuate the reversing switch 71 in one direction and a spring 72 to operate same in the opposite direction. In

normal cutting operation with the resistance of the submerged cutting arc in the cutting circuit, the spring 72 overcomes the pull of voltage coil 70, but if the cutting circuit is shorted permitting the line voltage to pass through the voltage coil, its pull overcomes spring 72 and reverses the motor by substituting the reverse'motor drive leads 73, 73 for the forward drivelead wires 74, 74. As'soon as the short circuit at the cutting electrode is broken'by the electrode being moved away from the work as a result of the'motor running in the opposite direction, the pull -of spring 72 again overcomes that of voltage coil 70, and the original condition is restored, and cutting proceeds.

It is'desirable, as when starting operations, in bringing the cutting electrode up to the work, or moving it in opposite di rection relative to the work, to be able to operate the motor in either direction without turning on the cutting current by switch 57. For this purpose I provide a second pair of motor circuits comprising wires 75, 75 for forward drive and 76, 76 for reverse drive, controlled by reversing switch 77 and having a current source (not shown) like the first described motor circuit, thus enabling the motor and electrode to be run in either direction independently of the cutting circuit. This switch 77 may be operated separately, or may be interconnected with switch 57, if desired, in such manner that but one of said switches may be in operative position at a time, as is diagrammatically indicated in the drawings in which switches 57 and 7 Tara pivoted to turn upon pivots oppositely located and are connected by a link 78. carrying a handle 79.

It will be seen that with the present invention' the electrical cutting of metals can be readily and effectively carried out and that very great advantages are secured in the economy of current consumption and ready control of the operation.

It is to be understood that the apparatus shown and described herein and the theories expressed are intended only for aifording an adequate understanding of the invention and the principle thereof andare not to impose limitations upon the invention, which is of the scope defined by my claims.

I claim:

1. The process of electrical cutting of metals which comprises cutting with low voltage current with the electrode in contact with the metal and slag whereby the cutting is done partially by are and partially by melting by current passage through localized high resistance.

2. The process of electrical cutting of 1 metals which comprises delivering current of low voltage and of high amperage to a small electrode area, keeping such area in mechanical contact with. the work and slag produced therefrom, whereby cutting is done artially by the electric arc and partially y melting of the metal by the passage of the electric current therethrough.

3. The method of electrical cutting in which the contact are is facilitated by a high localized resistance at the point to be cut, either bv the material or electrode being supplied with characteristics productive of such high localized resistance.

4. An electrode for electrical cutting of metals, the advancing face whereof is of relatively small dimension as compared with its cross-section.

5. An electrode for electrical cutting of metals having one dimension of its cross section at least twice its other dimension, the cutting face being upon the dimension last named.

6. An electrode for electrical cutting of metals which is substantially thin in cross section, one dimension of such cross section being several times the other, and the cutting face being upon the dimension last named.

7 A thin electrode for low voltage electrical cutting of metals having a width several times its thickness, and the thin edge being adapted to be held against the work, thereby a small area working surface is secured and at the same time the electrode is of sufiicient cross-section at and behind the working surface to provide sufficient current density at the contact surface without un dueburning out.

8. An electrode for low voltage electrical cutting of metals, comprising a rincipal portion of material of high electrical conductivity, and a removable and replaceable cutting portion carried by the first named portion.

9. An electrode for low voltage electrical cutting of metals, comprising a water-cooled hollow bar of copper or the like material,

and a facing of material such as graphite re movabl and replaceably secured to the forward e ge thereof.

10. A copper electrode for electrical metal cutting, faced on the cutting side with graphite 'or the like.

11. A water-cooled metallic electrode havin a dovetail formed therein, and a facing of high resistance electrode material having a dovetail groove formed therein and removably secured to the metallic portion of the electrode by said dovetail being received in said groove.

12. Ap aratus for electrical cutting of metals which comprises a. cutting electrode, an electrical motor for advancing said electrode relative to the work, and means for automatically reversing the motor when the cutting circuit is shorted.

13. Apparatus for electrical cutting of metals which comprises a cutting electrode, an alternating current motor for moving the electrode relative to the work, means for reversing the motor when the cutting circuit is shorted, and means for re-reversing the motor when the short circuit is broken.

14. In apparatus for electrical cutting of metals, a cutting electrode, an alternating current motor for moving same relative to work being cut, a reversing switch for the 7 motor, a spring for moving the switch to reverse position, and a voltage coilfor moving the switch to ahead position, said spring being adapted to overcome the pull of the voltage coil and reverse the motor when the cutting circuit is shorted, and the voltage coil being adapted to actuate said switch in opposition to said spring to re-reverse the motor when the short circuit is broken.

15. In apparatus for electrical cutting of metal, a cutting electrode and a low voltage cutting circuit including said electrode and the work, an alternating current motor adapted to move the electrode relative to the work, a reversing switch for the motor, a.

volta coil responding to the flow of current t rough the cutting circuit and adapted to position said switch for forward running of the motor when a substantial drop in voltage takes place at the cutting point, and a spring for actuating said switch to reverse the motor temporarily when thefcutting circuit is shorted.

16. In apparatus metals, a cutting electrode, a low voltage cutting circuit including the electrode and work, an alternating current motor for moving the electrode relative. to the work, a motor circuit, interconnected switches in the motor circuit and cutting. circuit whereby one cannot be closed unless the other is open, asecond motor circuit supplied from the cutting circuit, and means in the last named circuit for automatically reversing the motor when the cutting circuit is shorted and re reversing same when the short circuit is broken.

17. An electrode for low voltage electrical cutting of metals comprising a water-cooled hollow bar of metallic material, and a fac ing1 of material such-as graphite removably an re laceably secured to t thereo In testimony that I claim the foregoing, I have signed my name hereto.

PERCY A. E. ARMSTRONG.

0 forward edge for electrical cutting 'of' 

